Earth Sciences Report 1984-02

Earth Sciences Report 1984-02

Geology of the Ryan-Fletcher Lakes district, Alberta

The bedrock geology in the study area consists of three major belts, from west to east: the granitoids, a migmatite zone and a granite gneiss belt adjacent to Lake Athabasca. The granitoid terrain is dominated by the Slave Granitoids accompanied by subordinate amounts of Arch Lake Granitoids and high-grade metasedimentary rocks. The migmatite zone consists of major belts of high-grade metasediments interspersed with granitoid masses, principally Wylie Lake Granitoids and Chipewyan Red Granite. The granite gneiss belt is represented by biotite and hornblende granite gneisses with minor amounts of high-grade metasediments, amphibolite and granitoids.

All the above crystalline rocks show the effects of an amphibolite to granulite facies metamorphism with subsequent regional retrogressive greenschist facies metamorphism. The regional trend of the foliation is north to north-northeasterly. A narrow band of prograde greenschist facies metasedimentary rock lies in fault contact with the granite gneisses along the shoreline of Lake Athabasca.

The bedrock has been affected by faults that trend either parallel or perpendicular to the regional foliation. A prominent, regional mylonitic zone trends north-northeast through the granite gneiss belt. Biotite and hornblende K-Ar age dates show that the region was subjected to an intensive thermal event connected with the Hudsonian Orogeny.

A Pleistocene continental glaciation has scoured the map region, leaving widespread evidence of glacial erosion and deposits typical of the Canadian Shield. Ice advance was from the east. Aeolian reworking of some of the glacial sands by storm winds from the southeast caused the formation of dunes accompanied by wind polish and abrasion on the bedrock surface. Mineralization is scattered, consisting of minor uranium mineral stains and chalcopyrite in association with the high-grade metasedimentary rock.